The present invention relates to variable displacement compressors, such as that used in an automobile air-conditioning apparatus, swash plates, and methods for hardening the swash plates.
Japanese Unexamined Patent Publication No. 8-159022 describes a typical variable displacement type compressor. The compressor has a housing that houses a crank chamber and rotatably supports a drive shaft. The drive shaft is connected to an external drive source such as an automobile engine. A clutch connects the drive shaft to the external drive source. The housing includes a cylinder block, which is provided with a plurality of cylinder bores. A single-headed piston is reciprocally accommodated in each cylinder bore.
A swash plate, which serves as a cam plate, is provided on the drive shaft and supported so that it inclines with respect to the drive shaft while rotating integrally with the drive shaft. The swash plate is coupled to each piston. A central bore is defined in the cylinder block. The central bore is connected to a suction passage, which draws refrigerant gas into a suction chamber from an external refrigerant circuit. A spool is accommodated in the central bore to open and close the suction passage in cooperation with the inclination of the swash plate. A hole extends through the swash plate. The drive shaft is inserted through the hole in the swash plate. A thrust bearing is arranged between the spool and the swash plate. The wall of the swash plate hole contacts the outer surface of the drive shaft and the rear surface of the swash plate abuts against the spool during inclination of the swash plate.
A displacement control valve is provided in either the suction chamber or a discharge chamber. The control valve changes the pressure of the crank chamber. The difference between the pressure of the crank chamber and the pressure in the cylinder bores varies the displacement of the compressor.
When the swash plate inclines, the swash plate slides along the drive shaft and the spool. Thus, abrasion occurs during the sliding. To resist the abrasion, part of the swash plate undergoes an induction hardening treatment. As shown in FIGS. 7(a) and 7(b), the swash plate 91 has projections 92 extending from two sides of the hole 93. When the swash plate 91 is fitted on the drive shaft, the projections 92 face toward a spool. A hole 93 extends through the center of the swash plate 91. The drive shaft is inserted through the hole 93. The hardening treatment is carried out on the wall of the hole 93 and on the surfaces of the projections 92.
Induction hardening is performed by inserting a coil 94 into the hole 93, as shown in FIG. 7(a).
However, hardening of the swash plate 91 in this manner causes the heating of the surfaces of the projections 92 to be inferior to that of the wall of the hole 93. This may result in the surfaces of the projections 92 having inferior durability due to insufficient hardening. Furthermore, the hardening of the surfaces of the projections 92 to an optimal state results in excessive heating of the wall of the hole 93. This may lead to cracking or melting of the wall of the hole 93. It may also lead to undesirable deformation of the hole 93.
These problems may be dealt with by providing another coil for the surface of the projection 92. However, this would cause excessive heating of the corner, or edge, between the wall of the hole 93 and the surfaces of the projections. In this case, the edge may crack or melt.